The present invention concerns a vehicle headlamp of the type that includes:
a support structure,
a light source mounted on the support structure,
a first thin transparent pane placed in a fixed position in front of the light source, and on which a number of micro-lenses are integrated with a matrix-like layout,
a second thin transparent pane facing the said first pane and separated from it, on which a number of micro-lenses are also integrated in a matrix-like fashion, such that for each micro-lens of the first pane there are one or more corresponding micro-lenses on the second pane, forming a subgroup of the matrix of the second pane, the said first pane and the said second pane being capable of movement with respect to each other in a direction that is substantially parallel to the optical axis of the headlamp and perpendicular to these panes, as well as in a direction that is orthogonal to it.
the headlamp also includes first actuator means for controlling movement in the direction of the optical axis and second actuator means for controlling the said movement in a direction orthogonal to the optical axis.
A headlamp of the above-indicated type is described and illustrated in European patent application EP-A-0 860 650 presented by the Applicant. In this known device, it is possible to change the characteristics of the light beam generated by the headlamp without the need for macroscopic movement of the mobile part of the headlamp. In fact, each minute relative movement between the two panes carrying the micro-lens arrays allows a different micro-lens of the second pane to be selectively aligned with each micro-lens of the first pane. In the case of the known device, the adjustment movement is achieved via traditional types of actuators, where each one includes an electric motor and a nut and lever mechanism for example.
The object of this invention is that of perfecting the previously proposed device, rendering it much simpler, lighter, less bulky and more efficient.
In order to achieve this objective, the subject of the invention is a vehicle headlamp of the type indicated at the beginning of this description, characterized in that the said first and second actuator means are constituted by shape memory actuators.
Shape memory actuators are known devices in themselves, which have found application in various fields. They make use of elements composed of metal alloys, typically nickel and titanium alloys, which possess the property of contracting when the temperature exceeds a predetermined transition value. The Applicant has already proposed various applications for shape memory actuators, such as for the adjustment of vehicle rear-view mirrors, or the adjustment of deflector plates in air conditioners for motor vehicles and similar for example. For instance, a shape memory actuator could be composed of a wire made of a shape memory material that is placed between a fixed structure and the controlled organ. Heating the wire beyond its transition temperature, which can be achieved by passing an electrical current through the wire for example, causes the wire to shorten and thus move the controlled organ in a first direction. The controlled organ returns to its initial position when the wire cools down, and this can be aided by providing an elastic means of return.
This invention refers to a specific application of shape memory actuators of the aforementioned type to a vehicle headlamp possessing the characteristics that have been indicated at the beginning of this description.
In a preferred form of embodiment, the headlamp in accordance with the invention includes a number of first shape memory actuators acting in the direction of the headlamp""s optical axis and which are positioned between a mobile pane of the headlamp and the fixed support structure. In addition, at least one other shape memory actuator is provided along the direction orthogonal to the optical axis to control movement of the mobile pane of the headlamp assembly in this direction.
The application of shape memory actuators has various advantages. First of all, in the headlamp in accordance with the invention, it is essential that any adjustment movement be effected without changing the parallelism between the two panes carrying the micro-lenses. In the headlamp in accordance with the invention, the said shape memory actuators are directly connected to the mobile pane of the device. Thus, each of them directly controls the position of the mobile pane in space and, since a positional transducer is associated with each actuator, typically a potentiometer that supplies a feedback signal to the control system relative to the position reached by the portion of the pane directly controlled by the actuator, the electronic control system that commands the various actuators is capable of checking in an extremely simple manner that the condition of parallelism between the two panes is maintained. This advantage derives from the possibility of providing at least two, typically three or four, shape memory actuators for adjustments along the optical axis, a situation that was not possible to realize in a device in line with known techniques due to the significant bulk of traditional actuators.
In a preferred form of embodiment, each of the shape memory actuators acting in the direction of the optical axis includes a wire having one end connected to the controlled pane and the other end connected to the tip of a sheath through which a shape memory wire passes and which has its other end anchored to the fixed structure. The device also includes an intermediate portion of telescopic tubular wire guide, through which the shape memory wire passes, and which is connected respectively, in an articulated manner, to a support mounted on the controlled pane and to the headlamp""s fixed support structure. These articulated connections ensure that the controlled pane can also be moved in a direction orthogonal to the direction of the headlamp""s optical axis, or rather in a direction within the plane of the pane, in addition to the possibility of moving in a direction perpendicular to the plane of the pane.